refactor(routes): move notifications to /admin/notifications, remove /manage

Moved /notifications to /admin/notifications to match admin-only access pattern. Updated NavBar bell icon and mobile menu links. Removed /manage route (leftover prototyping). Pre-hydration redirect already in place for admin-only guard.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

frontend/src/lib/components/layout/NavBar.svelte

@@ -142,7 +142,7 @@
 			<div class="hidden items-center gap-4 md:flex">
 				{#if isAuthenticated}
 					<a
-						href={resolve('/notifications')}
+						href={resolve('/admin/notifications')}
 						class="relative text-gray-600 hover:text-primary"
 						aria-label="Notifications"
 					>
@@ -236,7 +236,7 @@
 
 				{#if isAuthenticated}
 					<a
-						href={resolve('/notifications')}
+						href={resolve('/admin/notifications')}
 						class="flex items-center justify-center gap-2 rounded px-3 py-2 text-primary hover:text-gray-800"
 					>
 						<span>Notifications</span>